docs/diploma

annotate thesis/tex/4-MasqmailsFuture.tex @ 150:0d097f4300ce

moved typographic conventions from ch01 to preface
author meillo@marmaro.de
date Tue, 16 Dec 2008 15:00:21 +0100
parents 2c4673d983c3
children 0b17f6e5edae
rev   line source
meillo@109 1 \chapter{\masqmail's present and future}
meillo@93 2
meillo@137 3 \section{Existing code base}
meillo@142 4 Here regarded is version 0.2.21 of \masqmail. This is the last version released by Oliver \person{Kurth}, and the basis for my thesis.
meillo@142 5
meillo@93 6
meillo@137 7 \subsubsection*{Features}
meillo@93 8
meillo@142 9 \masqmail\ accepts mail on the command line and via \SMTP. Mail queueing and alias expansion is supported. \masqmail\ is able to deliver mail to local mailboxes (in \name{mbox} or \name{maildir} format) or pass it to a \name{mail delivery agent} (like \name{procmail}). Mail destinated to remote locations is sent using \SMTP\ or can be piped to commands, being gatesways to \NAME{UUCP} or \NAME{FAX} for example.
meillo@93 10
meillo@142 11 Outgoing \SMTP\ connections feature \SMTP-\NAME{AUTH} and \SMTP-after-\NAME{POP} authentication, but incoming connections do not. Using wrappers for outgoing connections is supported. This offers a two way communication through a wrapper application like \name{openssl}.
meillo@137 12 %todo: what about SSL/TLS encryption?
meillo@93 13
meillo@142 14 \masqmail\ focuses on non-permanent online connections, thus a concept of online routes is used. One may configure any amount of routes to send mail. Each route can have criterias, like matching \texttt{From:} or \texttt{To:} headers, to determine if mail is allowed to be sent using it. Mail to destinations outside the local net gets queued until \masqmail\ is informed about the existance of a online connection.
meillo@142 15
meillo@137 16 The \masqmail\ executable can be called under various names for sendmail-compatibility reasons. This is organized by symbolic links with different names pointing to the \masqmail\ executable. The \sendmail\ names are \path{/usr/lib/sendmail} and \path{/usr/sbin/sendmail} because many programs expect the \mta\ to be located there. Further more \sendmail\ supports calling it with a different name instead of supplying command line arguments. The best known of this shortcuts is \path{mailq}, which is equivilent to calling it with the argument \verb+-bq+. \masqmail\ recognizes the names \path{mailq}, \path{smtpd}, \path{mailrm}, \path{runq}, \path{rmail}, and \path{in.smtpd}. The first two are inspired by \sendmail. Not implemented is the name \path{newaliases} because \masqmail\ does not generate binary representations of the alias file.\footnote{A shell script located named \path{newaliases}, that invokes \texttt{masqmail -bi}, can provide the command to satisfy other software needing it.} \path{hoststat} and \path{purgestat} are missing for sendmail-compatibility.
meillo@109 17 %masqmail: mailq, mailrm, runq, rmail, smtpd/in.smtpd
meillo@109 18 %sendmail: hoststat, mailq, newaliases, purgestat, smtpd
meillo@109 19
meillo@137 20 Additional to the \mta\ job, \masqmail\ also offers mail retrieval services with being a \NAME{POP3} client. It can fetch mail from different remote locations, dependent on the active online route.
meillo@109 21
meillo@137 22
meillo@137 23
meillo@137 24 \subsubsection*{The code}
meillo@137 25
meillo@137 26 \masqmail\ is written in the C programming language. The program, as of version 0.2.21, consists of 34 source code and eight header files, containing about 9,000 lines of code\footnote{Measured with \name{sloccount} by David A.\ Wheeler.}. Additionally, it includes a \name{base64} implementation (about 300 lines) and \name{md5} code (about 150 lines). For systems that do not provide \name{libident}, this library is distributed as well (circa 600 lines); an available shared library however has higher precedence in linking.
meillo@137 27
meillo@137 28 The only mandatory dependency is \name{glib}---a cross-platform software utility library, originated in the \NAME{GTK+} project. It provides safer replacements for many standard library functions. It also offers handy data containers, easy-to-use implementations of data structures, and much more.
meillo@137 29
meillo@109 30
meillo@109 31 With \masqmail\ comes the small tool \path{mservdetect}; it helps setting up a configuration that uses the \name{mserver} system to detect the online state. Two other binaries get compiled for testing purposes: \path{readtest} and \path{smtpsend}. All three programms use \masqmail\ source code; they only add a file with a \verb+main()+ function each.
meillo@109 32
meillo@93 33
meillo@137 34 \masqmail\ does not provide an interface to plug in modules with additional functionality. There exists no add-on or module system. The code is only separated by function to the various source files. Some functional parts can be included or excluded by defining symbols. Adding maildir support at compile time, means giving the option \verb+--enable-maildir+ to the \path{configure} call. This preserves the concerning code to get removed by the preprocessor. Unfortunately the \verb+#ifdef+s are scattered through all the source, leading to a FIXME(holperig) code base.
meillo@93 35
meillo@132 36
meillo@132 37
meillo@132 38
meillo@132 39
meillo@146 40
meillo@146 41 \section{Requirements}
meillo@146 42
meillo@146 43 Following is a list of current and future requirements to make \masqmail\ ready for the future.
meillo@146 44
meillo@146 45
meillo@146 46 \subsubsection*{Large message handling}
meillo@149 47 Trends in the market for electronic communication go towards consolidated communication, hence email will be used more to transfer voice and video messages. This leads to larger messages. The store-and-forward transport of email is not good suited for large data. Thus new protocols, like \NAME{QMTP} (described in section \ref{}), may become popular.
meillo@146 48
meillo@146 49
meillo@146 50 \subsubsection*{Ressource friendly software}
meillo@149 51 The merge of communication hardware and the move of email services from providers to homes, demands smaller and more resource-friendly software. The amount of mail will be lower, even if much more mail will be sent. More important will be the energy consumption and heat emission. These topics increased in relevance during the past years and they are expected to become more central. \masqmail\ is not a program to be used on large servers, but to be used on small devices. Thus focusing on energy and heat, not on performance, is the direction to go.
meillo@146 52
meillo@146 53
meillo@146 54 \subsubsection*{New mail transfer protocols}
meillo@149 55 Large messages demand more efficient transport through the net. As well is a final solution needed to defeat the spam problem. New mail transport protocols may be the only good solutions for both problems. They also can improve reliability, authentication, and verification issues. \masqmail\ should be able to support new protocols as they appear and are used.
meillo@146 56
meillo@146 57
meillo@149 58 \subsubsection*{Spam handling}
meillo@149 59 Spam is a major threat. According to the \NAME{SWOT} analysis, the goal is to reduce it to a bearable level. Spam fighting is a war are where the good guys tend to lose. Putting too much effort there will result in few gain. Real success will only be possible with new---better---protocols and abandonning the weak legacy technologies. Hence \masqmail\ should be able to provide state-of-the-art spam protection, but not more.
meillo@146 60
meillo@146 61
meillo@146 62 \subsubsection*{Easy configuration}
meillo@149 63 Having \mta{}s on many home servers and clients, requires easy and standardized configuration. The common setups should be configurable with single actions by the user. Complex configuration should be possible, but focused must be the most common form of configuration: choosing one of several standard setups.
meillo@146 64
meillo@146 65
meillo@146 66
meillo@146 67
meillo@146 68
meillo@146 69
meillo@146 70
meillo@137 71 \section{Directions to go}
meillo@132 72
meillo@146 73 This section discusses about what shapes \masqmail\ could have---which directions the development could go to.
meillo@132 74
meillo@132 75
meillo@137 76
meillo@137 77
meillo@149 78 \subsection{Access and Auth}
meillo@149 79
meillo@149 80 easiest: restricting by static IP addresses (Access control via hosts.allow/hosts.deny)
meillo@149 81 if dynamic remote hosts need access: some auth is needed
meillo@149 82 - SASL
meillo@149 83 - POP/IMAP: pop-before-smtp, DRAC, WHOSON
meillo@149 84 - TLS (certificates)
meillo@149 85
meillo@149 86 ``None of these add-ons is an ideal solution. They require additional code compiled into your existing daemons that may then require special write accesss to system files. They also require additional work for busy system administrators. If you cannot use any of the nonauthenticating alternatives mentioned earlier, or your business requirements demand that all of thyour users' mail pass through your system no matter where they are on the Internet, SASL is probably the solution that offers the most reliable and scalable method to authenticate users.'' (Dent: Postfix, page 44, ch04)
meillo@149 87
meillo@149 88
meillo@149 89
meillo@149 90 postfix: after-queue-content-filter (smtp communication)
meillo@149 91 exim: content-scan-feature
meillo@149 92 sendmail: milter (tcp or unix sockets)
meillo@149 93
meillo@149 94 checks while smtp dialog (pre-queue): in MTA implemented (need to be fast)
meillo@149 95 checks when mail is accepted and queued: external (amavis, spamassassin)
meillo@149 96
meillo@149 97 anti-virus: clamav
meillo@149 98
meillo@149 99 AMaViS (amavisd-new): email filter framework to integrate spam and virus scanner
meillo@149 100 internet -->25 MTA -->10024 amavis -->10025 MTA --> reciptient
meillo@149 101 | |
meillo@149 102 +----------------------------+
meillo@149 103 mail scanner:
meillo@149 104 incoming queue --> mail scanner --> outgoing queue
meillo@149 105
meillo@149 106 mimedefang: uses milter interface with sendmail
meillo@149 107
meillo@137 108
meillo@137 109
meillo@132 110 \subsection{Architecture}
meillo@132 111
meillo@149 112 The programs architecture is maybe the most influencing design decision with the greatest impact on the programs further capabilities. %fixme: search quote ... check if good
meillo@149 113
meillo@149 114 \masqmail's current artitecture is monolitic like \sendmail's and \exim's. But more than the other two, is it one block of interweaved code. \sendmail\ provides, with its \name{milter} interface, standardized connection channels to external modules. \exim\ has a highly structured code with many internal interfaces, like the one for supported authentication ``modules''. \masqmail\ has none of them.
meillo@149 115
meillo@149 116 Figure \ref{fig:masqmail-arch} is an attempt to depict \masqmail's internal structure.
meillo@149 117
meillo@149 118 \begin{figure}
meillo@149 119 \begin{center}
meillo@149 120 \input{input/masqmail-arch.tex}
meillo@149 121 \end{center}
meillo@149 122 \caption{Internal architecture of \masqmail}
meillo@149 123 \label{fig:masqmail-arch}
meillo@149 124 \end{figure}
meillo@149 125
meillo@149 126
meillo@132 127
meillo@146 128 (ssl)
meillo@146 129 -> msg-in (local or remote protocol handlers)
meillo@146 130 -> spam-filter (and more)
meillo@146 131 -> queue
meillo@146 132 -> msg-out (local-delivery by MDA, or remote-protocol-handlers)
meillo@146 133 (ssl)
meillo@132 134
meillo@132 135 A design from scratch?
meillo@132 136
meillo@140 137 << what would be needed (effort) >>
meillo@132 138
meillo@140 139 << would one create it at all? >>
meillo@132 140
meillo@140 141 << should it be done? >>
meillo@132 142
meillo@132 143 http://fanf.livejournal.com/50917.html %how not to design an mta - the sendmail command
meillo@132 144 http://fanf.livejournal.com/51349.html %how not to design an mta - partitioning for security
meillo@132 145 http://fanf.livejournal.com/61132.html %how not to design an mta - local delivery
meillo@132 146 http://fanf.livejournal.com/64941.html %how not to design an mta - spool file format
meillo@132 147 http://fanf.livejournal.com/65203.html %how not to design an mta - spool file logistics
meillo@132 148 http://fanf.livejournal.com/65911.html %how not to design an mta - more about log-structured MTA queues
meillo@132 149 http://fanf.livejournal.com/67297.html %how not to design an mta - more log-structured MTA queues
meillo@132 150 http://fanf.livejournal.com/70432.html %how not to design an mta - address verification
meillo@132 151 http://fanf.livejournal.com/72258.html %how not to design an mta - content scanning
meillo@132 152
meillo@132 153
meillo@146 154 \subsubsection*{local mail delivery}
meillo@146 155 But for example delivery of mail to local users is \emph{not} what \mta{}s should care about, although most \MTA\ are able to deliver mail, and many do. (\name{mail delivery agents}, like \name{procmail} and \name{maildrop}, are the right programs for this job.)
meillo@132 156
meillo@132 157
meillo@132 158
meillo@132 159
meillo@132 160
meillo@132 161
meillo@132 162
meillo@149 163 \subsection{spam and malicious content}
meillo@149 164
meillo@149 165 The same for malicious content (\name{malware}) like viruses, worms, trojan horses. They are related to spam, but affect the \MTA less, as they are in the mail body.
meillo@149 166
meillo@149 167 message body <-> envelope, header
meillo@149 168
meillo@149 169 where to filter what
meillo@149 170
meillo@149 171
meillo@93 172
meillo@93 173
meillo@99 174
meillo@93 175
meillo@93 176
meillo@93 177
meillo@146 178
meillo@146 179
meillo@146 180
meillo@146 181 \subsubsection*{\masqmail\ in five years}
meillo@146 182
meillo@146 183 Now how could \masqmail\ be like in, say, five years?
meillo@146 184
meillo@146 185 << plans to get masqmail more popular again (if that is the goal) >>
meillo@146 186
meillo@146 187 << More users >>
meillo@146 188
meillo@146 189
meillo@146 190
meillo@146 191
meillo@93 192 \section{Work to do}
meillo@93 193
meillo@146 194 << short term goals --- long term goals >>
meillo@146 195
meillo@140 196 << which parts to take out and do within the thesis >>
meillo@93 197